IBM researchers develop next-generation chip-cooling technologies

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London, 26 October 2006A Power and Cooling Summit here today, IBM (NYSE: IBM) researchers
presented an innovative approach for improving the cooling of computer
chips, an increasingly urgent need given the large amount of heat
released by today's more powerful processors and the additional
energy required for removing that heat.

The technique, called "high thermal conductivity interface
technology," allows a twofold improvement in heat removal over
current methods. This paves the way for continued development of
creative electronic products through the use of more powerful chips
without complex and costly systems simply to cool them.

As chip performance continues to progress according to Moore's
Law, efficient chip cooling has become one of the most vexing problems
for designers of electronic products. The IBM technique outlined
today is one of several being explored by scientists from IBM Research - Zurich to address the issue.

"Electronic products are capable of amazing things, largely
because of the more powerful chips at their heart," said Bruno
Michel, manager of the Advanced Thermal Packaging research group
at IBM's Zurich lab. "We want to help electronics makers keep
the innovations coming. Our chip-cooling technology is just one
tool at our disposal to help them do that."

The approach used by IBM addresses the connection point between
the hot chip and the various cooling components used today to draw
the heat away, including heat sinks. Special particle-filled viscous
pastes are typically applied to this interface to guarantee that
chips can expand and contract owing to the thermal cycling. This
paste is kept as thin as possible in order to transport heat from
chip to the cooling components efficiently. Yet, squeezing these
pastes too thin between the cooling components and chip would damage
or even crack the chip if the conventional technologies are used.

Using sophisticated micro-technology, the IBM researchers developed
a chip cap with a network of tree-like branched channels on its
surface. The pattern is designed such that when pressure is applied,
the paste spreads much more evenly and the pressure remains uniform
across the chip. This allows the right uniformity to be obtained
with nearly two times less pressure, and a ten times better heat
transport through the interface.

This unique and extremely powerful design for chip cooling is borrowed
from biology. Systems of hierarchical channels can be found manifold
in nature, e.g. tree leaves, roots, or the human circulatory system.
They can serve very large volumes with little energy, which is crucial
in all organisms larger than a few millimeters. Ancient water irrigation
systems also used the same approach.

The demonstrated prototype is part of a large effort within IBM's
Research and Development organizations to improve cooling performance
of next and future generations of computer systems.

The cooling bottleneck results from the demand for ever more powerful
computer chips and becomes one of the most severe constraints of
overall chip performance. Today's high-performance chips already
generate a power density of 100 Watts per square centimeter 
one order of magnitude more than that of a typical hotplate. Tomorrow's
chips may attain even higher power densities, which would create
surface temperatures close to that of the sun when not cooled (approx.
6000 °C). Current cooling technologies, mainly based on forced
air convection (fans) blowing across heat sinks with densely spaced
fins, have essentially reached their limits with the current generation
of electronic products. To make matters worse, energy needed to
cool computer systems is rapidly approaching the power used for
calculations, thus almost doubling the overall power budget.

"Cooling is a holistic challenge from the individual transistor
to the datacenter. Powerful techniques, brought as close as possible
to the chip right where the cooling is needed, will be crucial for
tackling the power and cooling issues," states Michel.

Looking beyond the limits of air-cooling systems, Zurich researchers
are taking their concept of branched channel design even further
and are developing a novel and promising approach for water-cooling.
Called direct jet impingement, it squirts water onto the back of
the chip and sucks it off again in a perfectly closed system using
an array of up to 50,000 tiny nozzles and a complicated tree-like
branched return architecture.

By developing a perfectly closed system, there is also no fear
of coolant getting into the electronics on the chips. What's more,
the IBM team was able to enhance the cooling capabilities of the
system by devising ways to apply it directly to the back of the
chip and thereby avoiding the resistive thermal interfaces in between
the cooling system and the silicon.

First lab results are impressive. The team has demonstrated cooling
power densities of up to 370 Watts per square centimeter with water
as coolant. This is more than six times beyond the current limits
of air-cooling techniques at about 75 Watts per square centimeter.
Yet, the system uses much less energy for pumping than other cooling
systems do.